Re: [PATCH 2/2] drm/i915/BXT: Tolerance at BXT DSI pipe_config comparison

[Ramalingam C <ramalingam.c@intel.com>]

On Thursday 31 March 2016 12:34 AM, Daniel Vetter wrote:
> On Wed, Mar 30, 2016 at 07:49:40PM +0530, Ramalingam C wrote:
>> On Wednesday 30 March 2016 05:02 PM, Daniel Vetter wrote:
>>> On Tue, Mar 29, 2016 at 11:04:51PM +0530, Ramalingam C wrote:
>>>> At BXT DSI, PIPE registers are inactive. So we can't get the
>>>> PIPE's mode parameters from them. The possible option is
>>>> retriving them from the PORT registers. But mode timing
>>>> parameters are progammed to port registers interms of byteclocks.
>>>>
>>>> The formula used to convert the pixels interms of byteclk is
>>>> 	DIV_ROUND_UP(DIV_ROUND_UP(pixels * bpp * burst_mode_ratio,
>>>>   						8 * 100), lane_count);
>>>>
>>>> So we retrieve them, interms of pixels as
>>>> 	DIV_ROUND_UP((clk_hs * lane_count * 8 * 100),
>>>> 					(bpp * burst_mode_ratio));
>>>>
>>>> Due to the multiple DIV_ROUND_UP in both formulas we get the worst
>>>> case delta in the retrieved PIPE's timing parameter as below
>>>> 	DIV_ROUND_UP((8 * intel_dsi->lane_count * 100),
>>>> 		(dsi_pixel_format_bpp(intel_dsi->pixel_format) *
>>>> 			intel_dsi->burst_mode_ratio)))
>>>>
>>>> This converson of byteclk to pixel is required for hsync, hfp and hbp.
>>>> Which intern impacts horrizontal timing parameters. At worst case to
>>>> get htotal all there parameters are added with hactive.
>>>> Hence delta will be 3 times of above formula. Hence this value is
>>>> considered as tolerance for pipe_config comparison, in case of BXT DSI.
>>>>
>>>> Signed-off-by: Ramalingam C <ramalingam.c@intel.com>
>>> This is the wrong way round imo, better would be to adjust the adjusted
>>> mode in the bxt dsi compute_config function to match the hw granularity.
>>> Stuff _really_ should match exactly, the fuzzy clock matching is mostly
>>> because our clock cod is a mess, and we can't/don't properly
>>> forward-compuate the actual clock timings we program into the hardware.
>>> -Daniel
>> Daniel, I got your point. But the problem will be that difficulty(even if
>> possible) in adjusting the adjusted mode parameters.
>> Reason is we are not programing the mode parameter as such. We will derive
>> the hfp, hsync and hbp from
>> hsync_start, hsync_end, hdisplay and htotal. These will be adjusted(divided
>> by 2) for dual link scenario.
>> And then resultant will go into the conversion as mentioned in the commit
>> message (two DIV_ROUND_UP onwards
>> and one DIV_ROUND_UP backwards). For this we have to make the parameter
>> divisible by three different factors.
>> So IMHO, even if this is possible, it will look more messy.
>>
>> Predicting the max error and tolerating it in pipe_config_compare will be
>> the straight forward and more reasonable.
>> Please let me know if i can go ahead in this approach.
> Yeah I discussed this some more with Jani on irc. I'd say we should store
> this adjusted horizontal timings (the ones fudged with burst_mode_ratio,
> lane_count, dual-link and all these things applied) into
> crtc_state->base.adjusted_mode. And then ofc also read those values out.
>
> The overall idea of the state verify/compare logic is that we start out
> with requested state from userspace, then derive the real hw state. And
> then compare that computed hw state with what's there already. Except for
> clocks, where there's special reasons, we never go back, since going back
> requires us to apply a range. This is the only way to guarnatee that "hw
> has the same exact mode programmed in both cases" iff "intel_crtc_state
> matches per intel_crtc_config_compare".
>
> state->adjusted_mode is never exposed to userspace, so there's no problem
> if it's has "strange" values. And we already have pipe_src_h/w to express
> the logical input rectangle.
>
> The idea is similar to how we set adjusted_mode.flags to what we actually
> program, instead of trying to make something up that's not perfectly
> accurate.
> -Daniel
Daniel,

I have tested by adjusting the adjusted_mode in set_dsi_timings() 
instead of intel_dsi_compute_config().
Reason is if we modify the adjusted mode at intel_dsi_compute_config() 
itself, then modified value will
be taken as input for set_dsi_timings. Hence the get_config will deviate 
further. I hope this should be fine with you and Jani.

This will work out, if set_dsi_timings() is called after the 
dsi_compute_config() on every suspend and resume or modeset.
I will verify this on Android once and update.

Please share your view on this, so that can update the patch with 
corresponding changes.
>
>>>> ---
>>>> Reviewed at https://lists.freedesktop.org/archives/intel-gfx/2016-March/089548.html
>>>>
>>>>   drivers/gpu/drm/i915/intel_display.c |   62 +++++++++++++++++++++++++++++++---
>>>>   1 file changed, 57 insertions(+), 5 deletions(-)
>>>>
>>>> diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
>>>> index c0627d6..282f036 100644
>>>> --- a/drivers/gpu/drm/i915/intel_display.c
>>>> +++ b/drivers/gpu/drm/i915/intel_display.c
>>>> @@ -12557,6 +12557,9 @@ intel_pipe_config_compare(struct drm_device *dev,
>>>>   			  bool adjust)
>>>>   {
>>>>   	bool ret = true;
>>>> +	struct intel_crtc *crtc = to_intel_crtc(current_config->base.crtc);
>>>> +	struct intel_encoder *intel_encoder;
>>>> +	struct intel_dsi *intel_dsi = NULL;
>>>>   #define INTEL_ERR_OR_DBG_KMS(fmt, ...) \
>>>>   	do { \
>>>> @@ -12593,6 +12596,54 @@ intel_pipe_config_compare(struct drm_device *dev,
>>>>   		ret = false; \
>>>>   	}
>>>> +/*
>>>> + * In case of BXT DSI, HW pipe_config will be retrieved from the port's timing
>>>> + * configuration. This retrival includes some errors due to the DIV_ROUND_UP.
>>>> + * So we are considering the max possible error at the comparison.
>>>> + */
>>>> +/*
>>>> + * htotal = hactive + hfp + hsync + hbp. Here last three lements might have
>>>> + * the converson error, hence we consider the 3 times of error as tolerance.
>>>> + */
>>>> +
>>>> +#define MAX_BXT_DSI_TIMING_RETRIVAL_ERR \
>>>> +		(intel_dsi == NULL ? 0 : \
>>>> +		DIV_ROUND_UP((3 * 8 * intel_dsi->lane_count * 100), \
>>>> +		(dsi_pixel_format_bpp(intel_dsi->pixel_format) * \
>>>> +			intel_dsi->burst_mode_ratio)))
>>>> +
>>>> +#define BXT_DSI_PIPE_CONF_CHECK_I_RANGE(name) { \
>>>> +	for_each_encoder_on_crtc(dev, &crtc->base, \
>>>> +					intel_encoder) { \
>>>> +		if (intel_encoder->type == INTEL_OUTPUT_DSI) { \
>>>> +			intel_dsi = enc_to_intel_dsi(&intel_encoder->base); \
>>>> +		} \
>>>> +	} \
>>>> +	if (!(current_config->name < pipe_config->name && \
>>>> +		current_config->name >= (pipe_config->name - \
>>>> +			MAX_BXT_DSI_TIMING_RETRIVAL_ERR))) { \
>>>> +		INTEL_ERR_OR_DBG_KMS("mismatch in " #name " " \
>>>> +		  "(expected %i, found %i(Err tolerance considered))\n", \
>>>> +		  current_config->name, \
>>>> +		  pipe_config->name); \
>>>> +		ret = false; \
>>>> +	} \
>>>> +}
>>>> +
>>>> +#define PIPE_CONF_CHECK_I_RANGE(name) { \
>>>> +	if (current_config->name != pipe_config->name) { \
>>>> +		if (IS_BROXTON(dev) && crtc->config->has_dsi_encoder) { \
>>>> +			BXT_DSI_PIPE_CONF_CHECK_I_RANGE(name) \
>>>> +		} else { \
>>>> +			INTEL_ERR_OR_DBG_KMS("mismatch in " #name " " \
>>>> +			  "(expected %i, found %i)\n", \
>>>> +			  current_config->name, \
>>>> +			  pipe_config->name); \
>>>> +			ret = false; \
>>>> +		} \
>>>> +	} \
>>>> +}
>>>> +
>>>>   #define PIPE_CONF_CHECK_M_N(name) \
>>>>   	if (!intel_compare_link_m_n(&current_config->name, \
>>>>   				    &pipe_config->name,\
>>>> @@ -12697,11 +12748,11 @@ intel_pipe_config_compare(struct drm_device *dev,
>>>>   	PIPE_CONF_CHECK_I(has_dsi_encoder);
>>>>   	PIPE_CONF_CHECK_I(base.adjusted_mode.crtc_hdisplay);
>>>> -	PIPE_CONF_CHECK_I(base.adjusted_mode.crtc_htotal);
>>>> -	PIPE_CONF_CHECK_I(base.adjusted_mode.crtc_hblank_start);
>>>> -	PIPE_CONF_CHECK_I(base.adjusted_mode.crtc_hblank_end);
>>>> -	PIPE_CONF_CHECK_I(base.adjusted_mode.crtc_hsync_start);
>>>> -	PIPE_CONF_CHECK_I(base.adjusted_mode.crtc_hsync_end);
>>>> +	PIPE_CONF_CHECK_I_RANGE(base.adjusted_mode.crtc_htotal);
>>>> +	PIPE_CONF_CHECK_I_RANGE(base.adjusted_mode.crtc_hblank_start);
>>>> +	PIPE_CONF_CHECK_I_RANGE(base.adjusted_mode.crtc_hblank_end);
>>>> +	PIPE_CONF_CHECK_I_RANGE(base.adjusted_mode.crtc_hsync_start);
>>>> +	PIPE_CONF_CHECK_I_RANGE(base.adjusted_mode.crtc_hsync_end);
>>>>   	PIPE_CONF_CHECK_I(base.adjusted_mode.crtc_vdisplay);
>>>>   	PIPE_CONF_CHECK_I(base.adjusted_mode.crtc_vtotal);
>>>> @@ -12779,6 +12830,7 @@ intel_pipe_config_compare(struct drm_device *dev,
>>>>   #undef PIPE_CONF_CHECK_X
>>>>   #undef PIPE_CONF_CHECK_I
>>>> +#undef PIPE_CONF_CHECK_I_RANGE
>>>>   #undef PIPE_CONF_CHECK_P
>>>>   #undef PIPE_CONF_CHECK_I_ALT
>>>>   #undef PIPE_CONF_CHECK_FLAGS
>>>> -- 
>>>> 1.7.9.5
>>>>
>>>> _______________________________________________
>>>> Intel-gfx mailing list
>>>> Intel-gfx@lists.freedesktop.org
>>>> https://lists.freedesktop.org/mailman/listinfo/intel-gfx
>> -- 
>> Thanks,
>> --Ram
>>

-- 
Thanks,
--Ram

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